Light-emissive devices, such as organic electroluminescent devices, are known, for example, from PCT/WO/13148 and U.S. Pat. No. 4,539,507. Such a device is illustrated in FIG. 1 and generally comprises: a substrate 2; a first electrode 4 disposed over the substrate 2 for injecting charge of a first plurality; a second electrode 6 disposed over the first electrode 4 for injecting charge of a second plurality opposite to said first plurality; an organic light-emissive layer 8 disposed between the first and second electrodes; and an encapsulant 10 disposed over the second electrode 6. In the arrangement shown in FIG. 1, the second electrode 6 and the encapsulant 10 are transparent so as to allow light emitted from the organic light-emissive layer 8 to pass therethrough. Such an arrangement is known as a top-emitting device. An example of a transparent encapsulant is a glass can encapsulant in which a sheet of glass having a cavity therein is disposed over the light-emissive structure comprising the electrodes and light-emissive layer. A further encapsulating layer may be provided in the form of a thin film encapsulant deposited over the upper surface of the top electrode.
Variations of the above-described structure are known. The first electrode may be the anode and the second electrode may be the cathode. Alternatively, the first electrode may be the cathode and the second electrode may be the anode. Other layers may be provided between the electrodes and organic light-emissive layer in order to aid charge injection and transport. Furthermore, a getter material may be disposed inside the cavity of the encapsulant 10 in order to absorb any moisture and oxygen and thus prolong the lifetime of the device. The electrodes and light-emissive layer (and any additional layers such as the charge injection and transport layers discussed above) constitute a light-emissive structure which may be pixelated in order to form a display comprising a plurality of emitting pixels. Methods of forming pixelated displays are well known in the art.
FIG. 2 shows a simplified schematic diagram illustrating a portion of a pre-form fabricated during manufacture of a plurality of electroluminescent devices. The pre-form comprises a common substrate 2 over which a plurality of anodes 4, organic electroluminescent material 8, and cathodes 6 are deposited to form a plurality of light-emissive structures. A common encapsulant 10 is disposed over the light-emitting structures and is adhered to the substrate 2 by lines of adhesive or solder. The encapsulant 10 comprises a sheet having a plurality of cavities formed therein, the cavities corresponding to the positions of the plurality of light-emissive structures. The pre-form is broken along lines (indicated as dashed lines in FIG. 2) between the plurality of light-emissive structures so as to produce a plurality of encapsulated light-emissive devices. A more complex sealing structure (not shown) may be provided to allow for easier breaking. For example lines of weakness may be provided by, for example, grooves, and/or the arrangement may be scribed prior to breaking in a scribe and break process.
Each light-emissive structure may comprise a single emitting component such as for use in a simple backlight. Alternatively, each light-emissive structure may comprise a plurality of pixels to form a display.
The pre-form is manufactured by depositing layers to form the light-emissive structures on the substrate and then adhering the prefabricated encapsulating sheet thereover.
FIG. 3 shows a portion of the prefabricated encapsulating sheet 10 which comprises a transparent sheet of material having a plurality of cavities 12 in one side thereof for receiving the light-emissive structures.
The method of manufacturing the encapsulating sheet is illustrated in FIG. 4. The cavities 12 are formed by etching the transparent sheet 10 in a first step 100. The etch step typically is carried out by sandblasting which produces a frosted surface 14 on the interior of the cavities 12 which is substantially opaque. In order to convert the frosted cavity glass into transparent cavity glass, the cavity glass is chemically milled (step 200) so as to etch away the frosted surface 14 in order to form cavities 12 having transparent surfaces 16.
A problem with the aforementioned manufacturing process is that the chemical milling step is very expensive. Furthermore, as the chemical milling process involves the removal of glass material, a thicker sheet of glass is required initially in order to provide an encapsulating sheet having sufficient strength to protect the underlying light-emissive structure in the final product. Furthermore, the chemicals used in the milling step are toxic and environmentally unfriendly.